Gas membrane separation processes have received attention in recent years because of their capability of achieving energy conservation when used as a process for separating CO2 from various gases such as natural or exhaust gases as well as synthetic gases that are synthesized in large-scale plants for hydrogen or urea production.
Various separation membranes have been hitherto proposed as gas separation membranes for use in these gas membrane separation processes. For example, it is proposed in Japanese Patent Laying-Open No. 08-193156 (PTD 1) that a CO2 separation membrane may be formed from a resin composition including a reaction mixture obtained by reacting a polyacrylic acid with a predetermined equivalent of aliphatic amine. It is proposed in Japanese Patent Laying-Open No. 2013-49048 (PTD 2) that a CO2-facilitated transport membrane may be made by depositing a gel layer onto a heat-resistant porous membrane, the gel layer having glycine and a deprotonating agent contained in a hydrogel membrane. In Japanese Patent Laying-Open No. 64-70125 (PTD 3), a method is proposed for separating gases by using an ion-exchange membrane made from a fluorine-containing polymer having an ion-exchange group with a weak acid or its salt and having a specified amount of ion-exchange capacity.